1. Field of the Invention
The present invention relates to a control apparatus for controlling a legged mobile robot such as a biped walking robot or the like.
2. Description of the Related Art
Legged moving robots such as biped walking robots which have a plurality of joints, including hip, knee, and ankle joints, in their legs have one or more actuators such as electric motors or the like in the respective joints. The actuators are connected to a controller mounted in the torso of the robot and are directly controlled in a centralized fashion by the controller.
Of those robot joints, the joints, such as the hip joints, near the proximal ends of the legs need to be combined with a large number of signal lines which connect the actuators in the other joints, such as the knee and ankle joints, closer to the distal ends of the legs to the controller. It is rather difficult to neatly arrange those signal lines at the joints near the proximal ends of the legs. The actuators spaced relatively remotely from the controller, e.g., the actuators associated with the ankle joints, tend to malfunction due to noise introduced into the signal lines by which those actuators are connected to the controller.
To overcome the above drawbacks, the applicant of the present application has attempted to construct the following control system, i.e., the so-called distributed-processing control system:
Local controllers for controlling the operation of the respective actuators are positioned near the actuators, respectively, and connected to the respective actuators by signal lines. A central controller is mounted in the torso of the robot for sequentially generating command data to determine actions, specifically angular displacements or like, of the actuators corresponding to the local controllers. The central controller is connected to the local controllers by bus lines to transmit command data from the central controller to the local controllers. The local controllers receive the command data, and control actual actions of the actuators, e.g., energize the actuators, based on the command data.
According to the above distributed-processing control system, since the local controllers are positioned near the actuators, signal lines between the local controllers and the actuators can be arranged easily and protected against the entry of noise. Furthermore, because the local controllers control actual actions of the actuators, the number of communication lines between the local controllers and the central controller may be small, and hence those communication lines can be arranged easily.
In the distributed-processing control system, each of the local controllers controls the operation of the corresponding actuator based on command data successively supplied from the central controller. If a local controller fails to receive normal command data due to a disconnection of the communication line between the local controller and the central controller, then the local controller fails to operate the actuator normally.
Upon such a failure, the leg of the robot malfunctions, causing the robot to fall, damaging the robot itself or an object that is hit by the robot. Particularly, if the robot is a biped walking robot, then the robot is highly likely to fall down when an actuator on a leg thereof fails to operate normally.
It is therefore an object of the present invention to provide a control apparatus for controlling a legged moving robot which incorporates a distributed-processing control system, to prevent the robot from falling down as much as possible even when any of local controllers for controlling operation of actuators on the legs of the robot fails to receive normal command data from a central controller.
To achieve the above object, there is provided in accordance with the present invention an apparatus for controlling a legged mobile robot having a plurality of actuators including at least actuators for moving legs thereof, comprising a plurality of local controllers disposed near and connected to the actuators, respectively, for controlling operation of the actuators, and a central controller connected to the local controllers for sequentially generating command data for controlling the operation of the actuators controlled by the local controllers and sending the generated command data to the local controllers, each of the local controllers comprising memory means for storing the command data sent from the central controller to the each local controller for a predetermined period, and means for monitoring a reception status of the command data in the each local controller and, in the event of a reception failure of the command data, controlling operation of the actuator corresponding to the each local controller based on the command data for the predetermined period in the past which have been stored in the memory means.
The memory means of each of the local controllers stores the command data for the predetermined period. When the local controller fails to receive normal command data from the central controller, i.e., suffers a reception failure, due to a disconnection of communication lines between the local controllers and the central controller, the local controller can predict, to a certain extent, an action to be performed by the actuator based on the command data for the predetermined period in the past which have been stored in the memory means. Consequently, in the event of a reception failure of the command data, the local controller controls operation of the actuator based on the stored command data for the predetermined period in the past to prevent the actuator from abruptly changing its action. As a result, the danger of the legged mobile robot to fall down is minimized.
The apparatus for controlling the legged mobile robot particularly lends itself to controlling a biped walking robot.
Each of the local controllers may comprise means for, in the event of a reception failure of the command data, determining a function approximating a time-dependent change of the command data for the predetermined period in the past which have been stored in the memory means, generating new command data according to the determined function, and controlling operation of the actuator corresponding to the each local controller based on the new command data.
Accordingly, in the event of a reception failure of the command data, new command data can be generated so as to predict normal command data to be received, depending on a time-dependent change of the command data for the predetermined period in the past which have been stored in the memory means. Thus, the actuator is prevented from abruptly changing its action, and can appropriately be controlled for desired operation.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate a preferred embodiment of the present invention by way of example.